Monomolecular natural films

Huhnerfuss H, Lange P, Walter W (1984) Wave damping by monomolecular surface films and their chemical stmcture. Part II Variation of the hydrophylic part of the film molecules including natural substances. J Mar Res 42 737-759... 

Since the 1960s natural surface films ( sea slicks ), that tend to exhibit thicknesses of one molecule only, have been in the focus of interdisciplinary research that required input by various disciplines such as oceanography, meteorology, physics and chemistry. Albeit the thickness of such monomolecular surface films is small compared to that of mineral oil films their wave damping capability and, thus, their influence on air-sea interactions is comparable. Consequently, they are still often mixed up with mineral oil films ( oil spills ), particularly in the Same of remote sensing applications. It is the aim of the present book to provide a scientific basis that allows avoiding such misinterpretation in the future. 

Langmuir, I. (1933) Oil lenses on water and the nature of monomolecular expanded films, J. Chem. Phys. 1, 756. 

The presence of water at the interface will cause interference with the establishment of a good bond. Some materials occurring as the substrate are hydrophilic in nature and will always attempt to achieve a monomolecular water film on their surfaces. This can occur, after the substrate has been cleaned and before the adhesive has been applied, from the atmosphere direct to the substrate surface, or later after the bond has been established, by diffusion. The presence of a water film at the interface can result in leaching of materials from the substrate which then can cause corrosion of the substrate, with resultant progressive loss of adhesion as corrosion spreads under the adhesive. 

The hydrophilic nature of the carboxyl group balanced against the hydrophobic nature of the hydrocarbon chain allows long-chain fatty acids to form monomolecular films at aqueous Hquid-gas, Hquid—Hquid, or Hquid—soHd interfaces (18). 

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

It is found that, even a monolayer of lipid (on water), when compressed can undergo various states. In the following text, the various states of monomolecular films will be described as measured from the surface pressure, n, versus area, A, isotherms, in the case of simple amphiphile molecules. On the other hand, the Il-A isotherms of biopolymers will be described separately since these have a different nature. 

This report describes the titration of monomolecular films of bovine serum albumin spread on supporting phases containing soluble detergents. The object was to compare the results of this study with those from titration studies of the pure protein, hoping that this comparison would permit a more detailed description of the nature of the binding sites of the complex. 

In mixed bilayer vesicles diacetylenic and natural lipids exhibit the same miscibility behavior as in monomolecular films. This can be demonstrated using differential scanning calorimetry (DSC). The neutral lipid (23) is immiscible with DSPC or DOPC as indicated by the two phase transitions of the mixed liposomes which occur at the same temperatures as those of the pure components (Fig. 33 a). 

Modern methods of vibrational analysis have shown themselves to be unexpectedly powerful tools to study two-dimensional monomolecular films at gas/liquid interfaces. In particular, current work with external reflection-absorbance infrared spectroscopy has been able to derive detailed conformational and orientational information concerning the nature of the monolayer film. The LE-LC first order phase transition as seen by IR involves a conformational gauche-trans isomerization of the hydrocarbon chains a second transition in the acyl chains is seen at low molecular areas that may be related to a solid-solid type hydrocarbon phase change. Orientations and tilt angles of the hydrocarbon chains are able to be calculated from the polarized external reflectance spectra. These calculations find that the lipid acyl chains are relatively unoriented (or possibly randomly oriented) at low-to-intermediate surface pressures, while the orientation at high surface pressures is similar to that of the solid (gel phase) bulk lipid. 

Qince the initial observation by Leathes (I) that cholesterol exerts a condensing effect on spread monomolecular films of natural lecithins,... 

Gibbs equation. The adsorption process involves the transport of molecules from the bulk solution to the interface, where they form a specially oriented monomolecular layer according to the nature of the two phases. When a Gibbs monolayer forms, it does not necessarily mean that the molecules are touching each other in this monolayer. Instead, if the anchoring from the sub-phase molecules is weak, the molecules may move freely in the two-dimensional interfacial area. Thus, the physically measurable monolayer area is sometimes much larger than the close-packed area where all the molecules touch each other. When any monolayer is fairly well populated with adsorbed molecules, it exerts a lateral spreading (film) pressure, it, which is equal to the depression of the surface tension (see Section 5.5.2). 

The nature of an oriented film of monomolecular thickness can be typically exemplified by the properties and behavior of stearic acid, one of the most thoroughly studied film-forming substances. Stearic acid (n-octadecanoic acid) in extended, rigid form has the molecular configuration seen in Fig. 10-1. The total chain length is 2.442 nm (24.42 8) and the cross-sectional area is 18.4 x 10 cm (16.4 82). A regularly packed array of these molecules, with their hydrocarbon chains adlineated and their carboxylic heads located as shown in Fig. 10-1, constitutes an oriented film of monomolecular thickness. The physical evidence for the existence and the nature of such films is well known and is described in the standard texts on the chemistry and physics of surfaces [6]. 

There are also scientific difficulties in approaching the problem of the entities formed in passivation. This is particularly so in the region of low electrode coverage, where there is no possibility of clearly distinguishing between the adsorbed or (monomolecular or less) oxide layer without an experimental method that is sufficiently sensitive and applicable situ. Experimental approach to the problem was for a long time connected with the measurement of electrochemical parameters, which usually measured an average current density and thus gave little information about the local current distribution, the nature and thickness of the passive film, and the film distribution over the surface. An... 

Self-assembled structures are quite suitable for studying the electronic behavior of ordered monomolecular films, and have contributed considerably to the provision of a better understanding of the quantum size nature of metal nanoparticles. On the other hand, it is quite clear that metal particles in future nanoelectronic devices should be in structures in which the QDs should not be self-arranged, but rather are... 

The idea that surfactant molecules preferentially orient at the oil-water interface not only helps clarify the picture of monomolecular film stabilization, but also sheds fight on the problem of explaining the emulsion type obtained as a function of the chemical structure of the adsorbed species. It was recognized early that the nature of the surfactant employed in the preparation of an emulsion could influence the type of emulsion formed. For example, while the alkali metal salts of fatty acid soaps normally produce o/w emulsions under a given set of circumstances, the use of di- and trivalent soaps often results in the formation of w/o systems. The invocation of a monolayer mechanism for the stabilization of emulsion droplets requires the formation of a relatively close-packed surfactant film at the interface, ft is clear, then, that the geometry of the adsorbed molecules must play an important role in the effect obtained. For efficiency of packing, it can be seen from Figure 11.6 that the formation of w/o systems with polyvalent soaps seems almost inevitable. 

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